(1) Field of the Invention
The invention relates to a spindle motor for disk drives, and more particularly to the spindle motor which has an improved magnetic arrangement to enhance the stability of the rotor motion.
(2) Description of the Prior Art
In the computer industry, the DVD/CD disk drive has been widely applied as a media storage/providing device. Further, three major parts of the disk drive are an optical reading/writing head, a spindle motor and a drive chipset, in which the spindle motor is the topic of this invention.
Referring to FIG. 1, a typical spindle motor 1 is shown, in which a left hand side of part 13 has been cross-sectional illustrated so as to reveal the composition of part 16 inside the part 13. As shown, the spindle motor 1 includes two major parts: a rotor 18 and a stator 16. Basically, the spindle motor 1 including both the rotor 18 and the stator 16 is symmetric in structure about a center line CL.
The rotor 18 rotating as a whole includes a spindle 12 as a rotational shaft of the rotor 18, a turntable 11 located symmetrically on top of the spindle 12 for bearing a disk 10, and a rotor bell 13 mounted symmetrically around the spindle 12. The rotor bell 13 providing an internal room 130 for accommodating major portion of the stator 16 further has an inner peripheral surface 133 for mounting a peripheral magnetic ring 14 and an open end 131 for allowing the stator 16 to enter.
The stator 16 includes a hollow shaft 161 having a central hole 160, and a plurality of protruding radial coil arms 162 as top-view shown in FIG. 2. One end (the bottom end) of the hollow shaft 160 is fixed at the printed circuit board 2 as well as a base plate 3 supporting the printed circuit board 2 thereupon, while another end is used to receive the spindle 12 of the rotor 18 and to allow the spindle 12 to spin in the central hole 160. The coil arms 162 of the stator 16 are located inside the rotor bell 13 without any contact with the peripheral magnetic ring 14 as well as any other part of the rotor bell 13. As shown, a coil 164 for generating an electrical field is constructed in a middle section of each coil arm 162.
As shown in FIG. 1, the printed circuit board 2 electrically and structurally connected with the stator 16 is mounted on the base plate 3 and is extended electrically by a flexible print circuit 4.
In application, the rotor 18 rotates about the stator 16.
In the art, it is well known that major concerns in design of the high-speed spindle motor 1 as shown in FIG. 1 are the noise, the lifetime and the precision. For example, a typical spindle motor for a 56× CD-ROM disk drive in the marketplace is usually operated at above 10,000 rpm. Under such a high-speed operation, any run-out or unbalance of the disk 10 carried by the spindle motor 1, caused by whatever reasons, will definitely result in some rotation turbulences or noises to the rotor 18 with respect to the stator 16, from which possible bias in optical tracking and focusing may end in failure of data retrieving or storing between the disk 10 and the optical reading/writing head (not shown in the figure).
In addition, the discrete features of the coil arms 162 of the stator 16 as shown in FIG. 2 will also cause inevitable switch noises to both the rotor 18 and relating electrical signals. Such switch noises will be even worse while meeting a disk run-out.
To improve the aforesaid problems occurred in the disk drive, it is easy to see that major efforts should be made on the spindle motor 1 who operates at high speeds and contributes mainly the dynamic characteristics to the disk drive.
Referring to FIG. 3, an effort to smooth out possible noises or disturbances happened to the rotor 18 is shown to have a top magnetic disk 15 installed within a shaft-top flange 163 of the stator hollow shaft 161. By providing the top magnetic disk 15 to the stator 16, a magnetic field between the top magnetic disk 15 and the inner roof surface 132 of the rotor bell 13, also symmetrically around spindle 12 of the rotor 18, can be established to act as a pseudo spring-and-damper combination for damping possible operation noises, i.e. absorbing unexpected disturbance energy to resume normal operation of the disk drive.
Yet, limited to the dimension and construction location at top of the hollow shaft 161, the top magnetic ring 15 can only provide a pretty local cone-shape magnetic field that effects only at a small area around the spindle 12 and thus that can't react efficiently and effectively to a significant run-out of the disk 10 over the turntable 11 as shown in FIG. 1.